Francis and Mrs Kirchner are long-time rivals: As leader of Argentina's Catholics, he had accused her populist government of demagoguery, while she called his position on gay adoptions reminiscent of the Middle Ages and the Inquisition.

But where the Falklands are concerned, Francis has been quoted as saying that Britain "usurped" the islands. Earlier this month, the islanders voted overwhelmingly to remain a British Overseas Territory.

Mrs Kirchner said she had asked for Francis' intercession to "facilitate dialogue" with Britain over the islands. Just last week British Prime Minister David Cameron said he did not agree with Francis' views on the Falklands. In asking Francis to intervene, Mrs Kirchner said she recalled how Pope John Paul II averted war in 1978 between Argentina and Chile over three tiny islands in the Beagle Channel at the southern tip of South America.

Mrs Kirchner also gave the new pope a gourd and straw, to hold the traditional Argentine tea that Francis loves, and he gave her a kiss. "Never in my life has a pope kissed me!" she said afterward. She called on the former Archbishop of Buenos Aires at his temporary home, the Vatican hotel, a day before she and other world leaders attend his installation Mass in St. Peter's Square that some estimates say could bring a million people to Rome.

The Vatican released details of the Mass, saying it would be a simplified version of the 2005 installation Mass that brought Pope Benedict XVI to the papacy, with many gestures to Eastern rite Catholics and Orthodox Christians in a sign of church unity. The Vatican also released details of Francis' coat of arms and official ring, both of which are in keeping with his simple style and harking back to popes past.

Francis will officially receive the ring and the pallium, a wool stole, during the installation Mass, which is drawing six sovereign rulers, 31 heads of state, three princes and 11 heads of government to the Vatican.

Mrs Kirchner and her predecessor and late husband, Nestor, defied church teaching to push through a series of measures with popular backing in Argentina, including mandatory sex education in schools, free distribution of contraceptives in public hospitals, and the right for transsexuals to change their official identities on demand. Argentina in 2010 became the first Latin American country to legalise same-sex marriages.

The Kirchner meeting is not the only diplomatic dance Francis will be conducting this week as more than 132 government delegations descend on Rome for the Mass formally installing Francis as the 266th leader of the 1.2-billion strong Catholic Church. One significant VIP is the spiritual leader of the world's Orthodox Christians, Ecumenical Patriarch Bartholomew I. His presence at the installation is the first from the Istanbul-based Patriarchate in nearly 1,000 years since the Great Schism divided the church in 1054.